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Abstract

We utilize advanced laser fields to clear a path through a dynamic turbid medium, a concept termed “Optical path clearing (OPC).” Particles are evacuated from a volume of the medium using the gradient and/or scattering forces due to an applied laser field with a suitably tailored spatial profile. Our studies encompass both an analytical model and proof-of-principle experiments where paths are cleared in dense bulk colloidal suspensions. Based on our results we suggest that high-performance and high efficiency OPC will be achieved by multiple-step clearing using dynamic laser fields based on Airy or inverted axicon beams.

Multiple Airy beam clearing. (a) Transverse beam intensity profile of an Airy beam. (b)–(d) Micrograph of colloidal sample (b) before, (c) shortly after and (d) ≈ 10 min after the clearing beams were switched on. The two squares indicate the initial position and size of the Airy beams, the lower on being oriented as shown in Fig. (a) and the upper one being flipped by 180°. The two arrows indicate the clockwise relocation of the two beams. Moreover the distance between the beams has been persistently increased throughout the course of the experiment yielding “hollowing” of the sample as shown in Fig. (d).

OPC in a dense bulk aqueous colloidal suspension using an inverted axicon beam. The beam propagates perpendicularly to the image plane. Particles are propelled and gathered on the beam’s bright ring as revealed by the dark ring-shaped shade occurring in the right-hand side figure.

Multiple Airy beams arranged on a triangular pattern. The red circle highlights the inner ring of beams which clear the central region from particles. The red arrows indicate the direction of transverse deflection during propagation of the respective beams.